1. Field of the Invention
The present invention relates to a fluorescent X-ray analysis apparatus which performs an element analysis and a composition analysis of a sample by irradiating a primary X-ray to the sample and detecting a fluorescent X-ray generated from the sample.
2. Description of the Related Art
In recent years, a cadmium pollution of a food, and the like become a problem, and a quantitative determination of a cadmium content in the food, and the like are performed. Hitherto, in the quantitative determination of cadmium, although there have been performed an IPC (induced plasma chromatography) and the like, there have been problems that, in addition to the fact that a time is necessary for such a pretreatment as to make the sample into a solution, a dispersion occurs in a measurement result in dependence on an operator. From the background like this, as a measurement method substituted for the IPC, a fluorescent X-ray analysis is noted. The fluorescent X-ray analysis is one in which a kind and a quantity of an element contained in the sample is specified by irradiating the primary X-ray to the sample and detecting the generated fluorescent X-ray, and hitherto it has been utilized mainly in an analysis of the sample, such as Cu alloy or Fe alloy, whose main component is a heavy element, and the like. Since the fluorescent X-ray has an energy inherent to the element, it is possible to specify the element having been contained in the sample and its quantity by detecting an energy and an intensity of the generated fluorescent X-ray. In the fluorescent X-ray analysis, there suffices if the primary X-ray is directly irradiated to the sample, and there are advantages that a measurement is possible even if the sample is not pretreated and, also as to an analysis result, a reproducibility is good in comparison with the IPC. A detection lower limit denoting an accuracy of the fluorescent X-ray analysis like this is determined by the following expression.
Here, the background intensity means an intensity of an X-ray generated mainly by a scattered ray or the like, which is other than the fluorescent X-ray generated from an aimed element having been contained in the sample, and it becomes a noise of the fluorescent X-ray. Further, the sensitivity is a magnitude of an obtainable X-ray intensity with respect to a concentration of an object element in the fluorescent X-ray analysis apparatus. That is, by decreasing the background intensity and further raising the sensitivity, the detection lower limit decreases, and it becomes possible to realize the quantitative determination of a trace element.
As the fluorescent X-ray analysis apparatus capable of performing the fluorescent X-ray analysis like this, for example, there is proposed one having possessed an X-ray source irradiating the primary X-ray to the sample, a detector detecting the fluorescent X-ray generated from the sample to which the primary X-ray has been irradiated, and a primary filter having plural filter components, or the like (see, e.g., JP-A-2004-150990 Gazette). According to the fluorescent X-ray apparatus like this, by absorbing the primary X-ray of plural energy bands by the primary filter and irradiating the primary X-ray of a necessary energy band, it is possible to decrease the background intensity, thereby improving the detection lower limit.
However, in the fluorescent X-ray analysis apparatus like the above, by causing the primary X-ray to transmit through the primary filter, the primary X-ray itself attenuates. Therefor, since an intensity of the fluorescent X-ray generated from the sample while being excited decreases as well, the intensity of the fluorescent X-ray obtainable by the detector decreases. That is, in the fluorescent X-ray analysis apparatus like the above, while it is possible to decrease the background intensity, the sensitivity decreases. Further, although it is also possible to raise the sensitivity by bringing the X-ray source and the detector close to an irradiation position of the sample, a separation distance between the X-ray source and the detector becomes short as well, so that there has been a limit in a raise of the sensitivity from a spatial limitation. Therefor, there has not led to obtain the detection lower limit capable of precisely measuring a trace aimed element in a light element such as a cadmium content in the food for instance.
This invention is one having been made in view of the above-mentioned circumstances, and one providing a fluorescent X-ray analysis apparatus in which the detection lower limit is improved, and it is possible to quantify the trace aimed element having been contained not only in the sample whose main component is the heavy element but also in the sample whose main component is the light element.